Volcanic Highlights of my Field Trip to California

Looks like I missed some Etna action over my week in the field, but I'll get to that later this week. However, I thought some images from the field trip to eastern California showing the volcanic highlights might be in order. Enjoy!

All images by Erik Klemetti

Red Hill Cinder Cone

One of our first stops in California was Red Hill Cinder Cone, near Fossil Falls. People don't tend to think about basaltic volcanism in California when places like Shasta, Lassen Peak and the Long Valley Caldera make all the news, but there are multiple volcanic fields that host a bevy of cinder cones. Red Hill is one of those Quaternary or younger cinder cones. It sits just to the west of the rhyolitic Coso dome field and both types of volcanism are related to the extension in the Basin and Range, where the crust under Owens Valley is thinned due to upwelling mantle material. Anytime you have upwelling mantle, you likely get melting of the mantle, producing basalts. Red Hill Cinder Cone is a manifestation of this magmatism. The cinder cone is being mined for, well, cinder, that is used to treat slippery roads and this shot caught the first light of day hitting its summit.

Big Pine Volcanic Field

Further north from Red Cinder is the Big Pine Volcanic Field, another cinder cone field that is the product of the basaltic magmas rising through the crust under Owens Valley, usually along faults on the edges of the valley. Research at the Big Pine Volcanic Field show that these basalts are sourced upwards of 45 km down.

Megacrysts

On the west side of the Owens Valley is the Sierra Nevada batholith, the solidified remains of a volcanic arc, specifically the magmatic systems beneath now eroded volcanoes. One of the spectacular features of the some of these granites are megacrysts, or giant crystals, found in the rocks. This megacryst was in a boulder near Lone Pine, California, far from its source. Many of the boulders strewn around the Owens Valley fault scarp in Lone Pine have these megacrystic potassium feldspars, some of which were over 10-12 cm across.

Panum Crater

At the very northern end of the Owens Valley lies Mono Lake and the Mono-Inyo crater chain. Near the southern shore of Mono Lake is Panum Crater, a small crater and dome formed in the last few hundred years. You can hike up to the top of the dome and along the way you will likely find these chunks of rhyolite that show beautiful breadcrust texture. This texture is due to the hot interior of these blocks continuing to expand while the cool exterior hardens and then cracks - a little bit like popcorn.

Mono Lake

This view across Mono Lake shows the famous tufas (freshwater carbonates) in the foreground. However, the volcanic stars of this image are the dark hill on the far side of the lake (Black Point) and the island in the middle (Paoha Island). Black Point formed when Mono Lake was much higher, likely around 12,000 years ago while Paoha Island is a cryptodome, a location where magma pushed its way towards the surface but never erupted. Paoha Island is mostly lake sediment pushed up and out of the lake, possibly as recently as 350 years ago.

Pumice Quarry, north of Bishop

One of the great aspects of the Long Valley caldera is how well exposed are many of the volcanic deposits. The students here are examining an outcrop of pumice flows and fallout from the ~0.76 Ma Bishop Tuff eruption. If you read the rocks carefully, you can see individual pyroclastic flows and the waxing/waning of the eruption, all likely occurring in the timescales of days to hours - probably better than being there when it happened!

Ubehebe Crater

After being stymied by construction during our department trip to Death Valley in 2010, we finally got to see Ubehebe Crater. This crater is the product of basalt rising through the crust and intersecting water near the surface - and that combination leads to explosions. If you look at the loose material that makes up the walls of the crater, you'd see a lot of clasts of the pre-existing bedrock mixed in with the new tephra (volcanic chunks), supporting the idea that these eruptions that likely occurred in the last few hundred to thousands of years were explosions.

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